Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous compounds, which may include nitrous oxides (NOx), and solid particulate matter, which may include unburned carbon particulates called soot.
Due to increased attention on the environment, exhaust emission standards have become more stringent. The amount of gaseous compounds emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of these engine emissions has been to implement exhaust gas recirculation (EGR). EGR systems recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas, which is redirected to the engine cylinder, reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder. The lowered maximum combustion temperature slows the chemical reaction of the combustion process, thereby decreasing the formation of nitrous oxides.
In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold by an EGR valve. However, the particulate matter in the recirculated exhaust gas can adversely affect the performance and durability of the internal combustion engine. As disclosed in U.S. Pat. No. 6,526,753 (the '753 patent), issued to Bailey on Mar. 3, 2003, a filter can be used to remove particulate matter from the exhaust gas that is being fed back to the intake air stream for recirculation. Specifically, the '753 patent discloses an exhaust gas regenerator/particulate capture system that includes a first particulate trap and a second particulate trap. A regenerator valve operates between a first position where an EGR inlet port fluidly connects a portion of an exhaust flow with the first particulate trap and a second position where the EGR inlet port fluidly connects the portion of the exhaust flow with the second particulate trap. The filtered EGR gases are then supplied for mixing with compressed air prior to or during entry into the intake manifold.
Although the exhaust gas regenerator/particulate capture system of the '753 patent may reduce the engine air pollutants exhausted to the environment while protecting the engine from harmful particulate matter, the exhaust gas regenerator/particulate capture system may be expensive and difficult to package. For example, because the exhaust gas regenerator/particulate capture system of the '753 patent must draw exhaust downstream of the first and second particulate traps and provide the recirculated exhaust flow to the intake manifold upstream of the engine, it may be large and awkward with extensive lengths of piping. This size coupled with the space required within the engine compartment to accommodate the exhaust gas regenerator/particulate capture system increases the cost of the exhaust gas regenerator/particulate capture system and the difficulty of retrofitting the exhaust gas regenerator/particulate capture system to older vehicles. In addition, the extensive lengths of piping and large particulate filters may create problematic flow restrictions.
The disclosed exhaust gas recirculation system is directed to overcoming one or more of the problems set forth above.